During the past year Phase I, Analysis of the Birthweight-Gestational Age Study has been completed. Phase I is concerned with the relationships of birthweight to placental weight, maternal education, socioeconomic index, gestation at registration, year of birth, institution, body length at birth and head circumference. Phase II, a multivariant analysis to determine the relationship of birthweight as the dependent variable to a large number of antecedent (prenatal) independent variables is in progress. The component variables of a Birthweight Index have been established and will be explored to determine its predictive value for birthweight-gestational age outcomes.